You may want to check the seam slippage of your beautiful fabric first, Thai silk is notorious in that regard.
Cut off 2 small pieces, sew them together and pull strongly on both sides of the seam. When the yarns of the fabrics ‘move’ and you can see the sewing thread, you have a problem. In that case, if you want to make a fitted garment, you’d have to underline it.
When it comes to washing, best to test it on a small piece too.